The 2012 UNEP Yearbook highlighted the problem of carbon in the soil and its impacts on the global environment. The PDF version of the specific chapter regarding soil carbon is available here. Soil carbon loss contributes to global environmental problems like land degradation and climate change.
Keeping Carbon in the Soil
Loss of carbon in the soil degrades the soil and change its ability to sustain agriculture and withstand shocks (like drought or floods). The problem is that human land use behavior is slowly but surely reducing the carbon in the soil. The report explains:
Since the 19th century, around 60 per cent of the carbon in the world’s soils and vegetation has been lost owing to land use. In the past 25 years, one-quarter of the global land area has suffered a decline in productivity and in the ability to provide ecosystem services because of soil carbon losses.
Human activities are the primary cause of the loss of carbon in the soil around the world. The report explains that:
Soil carbon stocks are highly vulnerable to human activities. They decrease significantly (and often rapidly) in response to changes in land cover and land use such as deforestation, urban development and increased tillage, and as a result of unsustainable agricultural and forestry practices.
The result of these various behaviors is a breakdown in the composition and strength of the soil. Without carbon, soil molecules do not link to one another as well as before; This Results in soil more susceptible to erosion/degradation and soil that cannot recover to extreme weather events. Loss of soil carbon:
leads to decreased cohesion between soil particles, which increases the susceptibility of soil to water or wind erosion, accelerates losses of bulk soil, and alters nutrient and water cycling. Degradation of soil structure reduces the soil volume for water storage and soil permeability for drainage. In turn, this can lead to greater volumes of overland flow, which exacerbates flooding and reduces groundwater recharge during rain events. Reduced groundwater recharge aggravates water shortages and drought conditions. Another consequence of soil carbon loss is the loss of soil nutrients.
Keeping carbon in the soil is thus of utmost importance for ecosystem and agricultural sustainability and resilience.
And Climate change…
More importantly is that the top meter of soil around the world contains three times the amount of carbon as exists in the atmosphere. Organic matter and decay in the soil creates large stocks of carbon in the soil. In addition to the focus of keeping carbon in the soil should be a focus on preventing it from moving into other systems.
Land use activities that breakdown carbon can release it into the atmosphere. The report explains:
Conversion of natural grasslands or forests to tilled soils breaks up soil aggregates, produces better aeration, and thus increases the decomposition of Soil Organic Matter and releases of CO2, with higher rates occurring in warm climates.
More drastic though is the, still not fully understood, possibility for soil carbon processes to increase significantly and contribute to additional atmospheric carbon. In permafrost areas, slight warming can contribute to significant transfer of soil carbon to the atmosphere. Schurr and Abbot explain in a paper in the December 2011 issue of Nature that:
Carbon released into the atmosphere from permafrost soils will accelerate climate change, but the magnitude of this effect remains highly uncertain. Our collective estimate is that carbon will be released more quickly than models suggest, and at levels that are cause for serious concern. We calculate that permafrost thaw will release the same order of magnitude of carbon as deforestation if current rates of deforestation continue. But because these emissions include significant quantities of methane, the overall effect on climate could be 2.5 times larger.
Although these are certainly not the primary problem of climate change, which will remain human use of fossil fuel resources, they present a particularly pernicious amplifier. Schurr and Abbot continue:
Permafrost carbon release … occurs in remote places, far from human influence, and is dispersed across the landscape. Trapping carbon emissions at the source — as one might do at power plants — is not an option. And once the soils thaw, emissions are likely to continue for decades, or even centuries.
A Global Soil Solution?
Is there a global solution to the various problems contributing to soil degradation around the world? The United Nations Convention Concerning Desertification is one attempt at dealing with the problem. However, the large problem is that soil degradation is an extremely local problem and any solution will have to be adopted in many different localities. In addition, the centralized agricultural ministries in many countries may prevent connections of local projects in efficient manners. Approaches to soil carbon require local creativity/specificity but a global effort toward the problem. The UNEP 2012 Yearbook presents an excellent step forward in this direction.